Lithium metal oxide electrodes for lithium cells and batteries

ABSTRACT

A lithium metal oxide positive electrode for a non-aqueous lithium cell is disclosed. The cell is prepared in its initial discharged state and has a general formula xLiMO 2 .(1-x)Li 2 M′O 3  in which 0&lt;x&lt;1, and where M is one or more trivalent ion with at least one ion being Mn or Ni, and where M′ is one or more tetravalent ion with at least one ion. Complete cells or batteries are disclosed with anode, cathode and electrolyte as are batteries of several cells connected in parallel or series or both.

RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. §1.78(a)(3) provisional application Serial No. 60/213,618 filed Jun. 22, 2000, the entire contents of which are incorporated herein by reference.

CONTRACTUAL ORIGIN OF THE INVENTION

[0002] The United States Government has rights in this invention pursuant to Contract No. W-31-109-ENG-38 between the U.S. Department of Energy (DOE) and The University of Chicago representing Argonne National Laboratory.

BACKGROUND OF THE INVENTION

[0003] This invention relates to lithium metal oxide positive electrodes for non-aqueous lithium cells and batteries. More specifically, it relates to lithium-metal-oxide electrode compositions and structures, having in their initial state in an electrochemical cell, a general formula xLiMO₂.(1-x)Li₂M′O₃ alternatively Li_(2-x)M_(x)M′_(1-x)O_(3-x) in which 0<x<1 and where M is one or more trivalent ion with at least one ion being Mn, and where M is one or more tetravalent ions selected preferably from Mn, Ti and Zr; or, where M is one or more trivalent ion with at least one ion being Ni, and where M′ is one or more tetravalent ion with at least one ion being Mn. In one embodiment of the invention, the Mn content should be as high as possible, such that the LiMO₂ component is essentially LiMnO₂ modified in accordance with this invention. In a further embodiment of the invention, the transition metal ions and lithium ions may be partially replaced by minor concentrations of one or more mono- or multivalent cations such as H⁺ derived from the electrolyte by ion-exchange with Li⁺ ions, and/or Mg²⁺ and Al³⁺ to impart improved structural stability or electronic conductivity to the electrode during electrochemical cycling.

SUMMARY OF THE INVENTION

[0004] Lithium-metal oxide compounds of general formula LiMO₂, where M is a trivalent transition metal cation Co, Ni, Mn, Ti, V, Fe, and with electrochemically inactive substituents such as Al are very well known and are of interest as positive electrodes for rechargeable lithium batteries. The best-known electrode material is LiCoO₂, which has a layered-type structure and is relatively expensive compared to the isostructural nickel and manganese-based compounds. Efforts are therefore being made to develop less costly electrodes, for example, by partially substituting the cobalt ions within LiCoO₂ by nickel, such as in LiNi_(0.8)Co_(0.2)O₂ or by exploiting the manganese-based system LiMnO₂. Such layered compounds are sometimes stabilized by partially replacing the transition metal cations within the layers by other metal cations, either alone or in combination. For example, Mg²⁺ ions may be introduced into the structure to improve the electronic conductivity of the electrode, or Al³⁺ or Ti⁴⁺ ions to improve the structural stability of the electrode at high levels of delithiation. Examples of such compounds are LiNi_(0.8)Co_(0.15)Al_(0.05)O₂ and LiNi_(0.75)Co_(0.15)Ti_(0.05)Mg_(0.05)O₂.

[0005] A major problem of layered LiMO₂ compounds containing either Co or Ni (or both) is that the trivalent transition metal cations, M, are oxidized during charge of the cells to a metastable tetravalent oxidation state. Such compounds are highly oxidizing materials and can react with the electrolyte or release oxygen. These electrode materials can, therefore, suffer from structural instability in charged cells when, for example, more than 50% of the lithium is extracted from their structures; they require stabilization to combat such chemical degradation.

[0006] Although the layered manganese compound LiMnO₂ has been successfully synthesized in the laboratory, it has been found that delithiation of the structure and subsequent cycling of the Li_(x)MnO₂ electrode in electrochemical cells causes a transition from the layered MnO₂ configuration to the configuration of a spinel-type [Mn₂]O₄ structure. This transformation changes the voltage profile of the Li/Li_(x)MnO₂ cell such that it delivers capacity over both a 4V and a 3V plateau; cycling over the 3V plateau is not fully reversible which leads to capacity fade of the cell over long-term cycling. Other types of LiMnO₂ structures exist, such as the orthorhombic-form, designated O-LiMnO₂ in which sheets of MnO₆ octahedra are staggered in zig-zig fashion unlike their arrangement in layered LiMnO₂. However, O-LiMnO₂ behaves in a similar way to layered LiMnO₂ in lithium cells; it also converts to a spinel-like structure on electrochemical cycling.

[0007] Therefore, further improvements must be made to LiMO₂ electrodes, particularly LiMnO₂, to impart greater structural stability to these electrode materials during electrochemical cycling in lithium cells and batteries. This invention addresses the stability of LiMO₂ electrode structures, particularly LiMnO₂, and makes use of a Li₂M′O₃ component to improve their stability.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.

[0009]FIG. 1 depicts a schematic representation of a Li₂M′O₃-MO₂-LiMO₂ phase diagram, in which M is a trivalent ion (or ions) and M is a tetravalent ion (or ions);

[0010]FIG. 2 depicts the X-ray diffraction pattern of a xLi₂MnO₃.(1-x)LiNi_(0.8)Co_(0.2)O₂ electrode composition;

[0011]FIG. 3 depicts the X-ray diffraction pattern of a xLi₂Mn_(1-x)Ti_(x)O₃.(1-x)LiNi_(0.8)Co_(0.2)O₂ electrode composition;

[0012]FIG. 4 depicts the X-ray diffraction pattern of a xLi₂TiO₃.(1-x)LiMnO₂ electrode composition;

[0013]FIG. 5 depicts the electrochemical profile of a Li/xLi₂MnO₃.(1-x)LiNi_(0.8)Co_(0.2)O₂ electrochemical cell;

[0014]FIG. 6 depicts the electrochemical profile of a Li/xLi₂TiO₃.(1-x)LiMnO₂ electrochemical cell;

[0015]FIG. 7 depicts a schematic representation of an electrochemical cell; and

[0016]FIG. 8 depicts a schematic representation of a battery consisting of a plurality of cells connected electrically in series and in parallel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] This invention relates to stabilized LiMO₂ electrodes whereby an electrochemically inert rocksalt phase Li₂MO₃ is introduced as a component to the overall electrode structure as defined, in its initial state, by the general formula xLiMO₂.(1-x)Li₂M′O₃ alternatively Li_(2-x)M_(x)M′_(1-x)O_(3-x) in which 0<x<1, preferably 0.8≦x<1, and more preferably 0.9≦x<1, and where M is one or more trivalent ions having at least one ion selected from Mn and where M′ is one or more tetravalent ion selected preferably from Mn, Ti and Zr, or alternatively, where M is one or more trivalent ions having at least one ion selected from Ni and where M′ one or more tetravalent ions having at least one ion selected from Mn. These compounds can be visualized as lying on the LiMO₂-Li₂M′O₃ tie-line of the Li₂M′O₃-MO₂-LiMO₂ phase diagram shown schematically in FIG. 1.

[0018] The rocksalt phase Li₂MnO₃ has a layered-type structure in which discrete layers of lithium ions alternate with layers containing Mn and Li ions (in a 2:1 ratio) between the close-packed oxygen sheets. Note that, in this respect, the formula Li₂MnO₃ can be written in layered notation as Li(Mn_(2/3)Li_(1/3))O₂, in which the Li and Mn within round brackets represent the ions in one layer. A difference between Li₂MnO₃ and the layered LiMO₂ compounds is that the Mn ions in Li₂MnO₃ are tetravalent and cannot be easily electrochemically oxidized by lithium extraction, whereas in the LiMO₂ compounds the transition metal cations M are trivalent and can be electrochemically oxidized. Because Li₂MnO₃ has a rocksalt phase, there is no energetically favorable interstitial space for additional lithium; therefore, Li₂MnO₃ cannot operate as an insertion electrode and cannot be electrochemically reduced. The xLiMO₂.(1-x)Li₂M′O₃ structure can be regarded essentially as a compound with a common oxygen array for both the LiMO₂ and Li₂MnO₃ components, but in which the cation distribution can vary such that domains of the two components exist side by side. Such a domain structure does not rule out the possibility of cation mixing and structural disorder, particularly at domain or grain boundaries. In a generalized xLiMO₂.(1-x)Li₂M′O₃ layered structure, one layer contains M, M′ and Li ions between sheets of close-packed oxygen ions, whereas the alternate layers are occupied essentially by lithium ions alone. By analogy, in a xLiMO₂.(1-x)Li₂M′O₃ structure that contains monoclinic LiMnO₂ as the LiMO₂ component, it is believed that the tetravalent M′ ions can partially occupy the M positions in the monoclinic layered LiMnO₂ structure, thereby providing increased stability to the overall structure.

[0019] Thus in the electrodes of the present invention, the M and M′ ions can be disordered in the electrode structure. It is preferable that the Mn content should be as high as possible, such that the LiMO₂ component is essentially LiMnO₂. In a further embodiment of the invention, the transition metal ions and lithium ions may be partially replaced by minor concentrations (typically less than 10 atom percent) of other mono- or multivalent cations such as Al³⁺ or Mg²⁺ to impart improved structural stability or electronic conductivity to the electrode during electrochemical cycling. In addition, the xLiMO₂.(1-x)Li₂M′O₃ structures of the invention may include H⁺ ions, for example, resulting from the removal acidic H⁺ species from the electrolyte by ion-exchange with Li⁺ ions. It stands to reason, therefore, and the present invention includes where to put that because of the introduction of mono- or divalent cations into the structure, the electrodes of the invention may depart slightly from the ideal stoichiometry as defined by the formula xLiMO₂.(1-x)Li₂M′O₃.

[0020] It has been shown in the past that Li₂MnO₃ (and isostructural Li₂Mn_(1-x)Zr_(x)O₃) which is electrochemically inactive, can be used as a precursor material to form an electrochemically active charged xMnO₂.(1-x)Li₂MnO₃ electrode structure in which x is approximately equal to 0.91; this value of x translates to a composition of the layered structure Li_(1.1)Mn_(0.9)O₂. These charged xMnO₂.(1-x)Li₂MnO₃ compounds have been prepared by leaching Li₂O from the Li₂MnO₃ (Li₂O.MnO₂) structure with acid such as sulphuric acid (U.S. Pat. No. 5,153,081). However, the acid treatment causes a shear of the oxygen array, such that the resulting xMnO₂.(1-x)Li₂MnO₃ structures are no longer close-packed but have an oxygen arrangement that provides octahedral and trigonal prismatic sites in alternate layers. During relithiation, for example with Lil in acetonitrile, it has been demonstrated that the oxygen sheets shear back to close-packing and that the phase transformation yields a xLiMnO₂.(1-x)Li₂MnO₃-type structure. However, such phase transformations are undesirable in rechargeable battery systems, because they can adversely affect the efficiency and rechargeability of the electrode. Thus, a major advantage of this invention is that this phase transformation can be avoided by starting directly with a discharged xLiMnO₂.(1-x)Li₂MnO₃ electrode in the cell because the non-aqueous removal of lithium does not appear to cause the phase transition to yield the structure generated by acid leaching of Li₂MnO₃ (non close-packed).

[0021] Furthermore, it is important to note that even though the relithiation of a xMnO₂.(1-x)Li₂MnO₃ electrode of the prior art in an electrochemical cell yields the same formulation as the electrodes of the present invention, i.e., xLiMnO₂.(1-x)Li₂MnO₃, the applicants believe that the structures of the electrode materials of the present invention are significantly different from those of the prior art and will be unequivocally distinguished from one another by high-resolution transmission electron microscopy, i.e., differences will be evident in the microstructural features of the xLiMnO₂-(1-x)Li₂MnO₃ electrodes of the present invention and those of the prior art. For example, because the lithiated 20 xLiMnO₂-(1-x)Li₂MnO₃ electrode structures of the prior art are derived from a non-close-packed xMnO₂-(1-x)Li₂MnO₃ structure, which is obtained by the acid leaching of, and Li₂ 0 removal from, a Li₂MnO₃ precursor as described above, the microstructures of the prior art electrode materials will be characterized by high concentrations of defects and stacking faults, as is evident by the broad peaks in their X-ray diffraction patterns, in contrast to the electrode materials of the present invention that are more crystalline and ordered as reflected by the relatively sharp and well-resolved peaks in their X-ray diffraction patterns (FIGS. 2,3 and 4).

[0022] Another disadvantage of the acid-treated compounds of the prior art ('081 patent) xMnO₂.(1-x)Li₂MnO₃, is that they represent charged positive electrodes, whereas lithium-ion batteries require positive electrodes in the discharged state, for example, LiMO₂ electrodes (M═Co, Ni, Mn). Moreover, the charged xMnO_(2.1)-x)Li₂MnO₃ electrodes of the prior art require dehydration before use so that they can be used effectively in lithium cells. By contrast, the xLiMnO₂.(1-x)Li₂MnO₃ electrodes of this invention are prepared in the discharged state and are essentially anhydrous materials and are more stable to heat-treatment and long-term storage in air compared to the xMnO₂.(1-x)Li₂MnO₃ materials of the prior art, which are known to transform on storage to a gamma-MnO₂-type structure as reported by Johnson et al in J. PowerSource 81-82, 491 (1999).

[0023] In one embodiment, this invention extends to include xLiMO₂.(1-x)Li₂M′O₃ electrodes stabilized by isostructural rocksalt Li₂M′₃ compounds other than M′═Mn, Ti, Zr as described in the preceding sections. Examples of such compounds are Li₂RuO₃, Li₂ReO₃, Li₂IrO₃, and Li₂PtO₃ which may contribute a portion of the electrochemical capacity of the electrode.

[0024] One of the difficulties that has been encountered in synthesizing xLiMO₂.(1-x)Li₂M′O₃ electrodes, in which M is Mn, has been to keep the valency of the manganese ions equal, or close to its trivalent state. This has been successfully accomplished by the inventors with a hydrothermal method or process under basic conditions using LiOH and/or KOH. This invention, therefore, extends to include a hydrothermal process or method for synthesizing xLiMO₂.(1-x)Li₂M′O₃ compounds in which M is one or more trivalent ion with at least one ion being Mn, and in which M′ is a tetravalent ion. Such methods of synthesis are undertaken in a pressurized autoclave, preferably between 5 and 35 atmospheres and at temperatures ranging between 100 and 250° C. and most preferably at 10-20 atm and temperatures between 180 and 230° C. for about 6 to 12 hours or more if necessary. For example, 0.15LiMnO₂.85Li₂TiO₃ electrodes have been successfully prepared by this process from precursor materials consisting of manganese oxide (Mn₂O₃), lithium hydroxide (LiOH.H₂O) and titanium isopropoxide (Ti[OCH(CH₃)₂]₄) in a potassium hydroxide (KOH) solution at 220° C. and at 15 atmospheres pressure.

[0025] It has been recently demonstrated that layered lithium-chromium-manganese-oxide and lithium-cobalt-manganese-oxide electrodes of general formula xLiCrO₂.(1-x)Li₂MnO3 and xLiCoO₂.(1-x)Li₂MnO₃ provide electrochemical stability when cycled between 4.5 and 2.0 V in electrochemical lithium cells. In particular, a Li(Cr_(0.4)Mn_(0.4)Li_(0.2))O₂ electrode (alternatively, 0.4LiCrO₂.0.4Li₂MnO₃) delivers approximately 150 mAh/g at 25° C. and 200 mAh/g at 55° C. at an average cell voltage of 3.5 V vs. Li. However, because the Li₂MnO₃ component is electrochemically inactive, the electrochemical capacity derived from the cell is due to the oxidation of Cr³⁺ to Cr⁶⁺ during the electrochemical charging of the cells. This system has an immediate disadvantage because it is known that the high oxidation states of chromium such as those found in Cr₃O₈ are dangerous and are a major health hazard whereas the electrodes of the present invention operate predominantly off a M³⁺/M⁴⁺ couple, notably a Mn³⁺/⁴⁺ couple. For the cobalt compound, xLiCoO₂.(1-x)Li₂MnO₃, no significant advantage is gained in overcoming the cost limitations of the electrode because the cobalt ions, not the manganese ions, provide all the electrochemical capacity of the electrode.

[0026] The following examples of stabilized xLiMnO₂.(1-x)Li₂MnO₃ electrodes containing either manganese and/or nickel describe the principles of the invention as contemplated by the inventors, but they are not to be construed as limiting examples.

EXAMPLE 1

[0027] The material 0.2Li₂MnO₃.0.8LiNi_(0.8)Co_(0.2)O₂ that can be written, alternatively, as Li(Ni_(0.58)Mn_(0.18)Co_(0.15)Li_(0.09))O₂ was prepared by the reaction of Ni(NO₃)₂, Co(NO₃)₂, MnO₂, and LiOH in the required stoichiometric amounts at 800° C. in air or oxygen for about 16 hours. The powder X-ray diffraction pattern of this compound indicates an essentially single-phase product with a layered-type structure (FIG. 2).

EXAMPLE 2

[0028] The material 0.2Li₂Mn_(1-x)Ti_(x)O₃.0.8LiNi_(0.8)Co_(0.2)O₂, where x=0.5, which can be written, alternatively, as Li(Ni_(0.58)Mn_(0.09)Ti_(0.09)Co_(0.15)Li_(0.09))O₂ was prepared by the reaction of Ni(NO₃)₂, Co(NO₃)₂, MnO₂, TiO₂ (anatase) and LiOH in the required stoichiometric amounts at 800° C. in air or oxygen for about 16 hours. The powder X-ray diffraction pattern of this compound indicates an essentially single-phase product with a layered-type structure (FIG. 3).

EXAMPLE 3

[0029] The material 0.15Li₂TiO₃.0.85LiMnO₂ that can be written, alternatively, as Li(Ti_(0.14)Mn_(0.79)Li_(0.07))O₂ was prepared by the hydrothermal reaction of Mn₂O₃, TiO₂ (anatase) and LiOH in the required stoichiometric amounts at 220° C. and 15 atmospheres pressure for about 10 hours. The powder X-ray diffraction pattern of this compound indicates an essentially single-phase product with a layered-type structure (FIG. 4).

EXAMPLE 4

[0030] The xLiMO₂.(1-x)Li₂M′O₃ electrode materials were evaluated in coin cells (size 2032) 20 mm diameter and 3.2 mm high against a counter lithium electrode. The cells had the configuration: Li/1M LiPF₆ in ethylene carbonate (EC), diethyl carbonate (DEC) (1:1 )electrolyte/xLiMO₂.(1-x)Li₂M′O₃, in which the xLiMO₂.(1-x)Li₂M′O₃ electrode consisted of 0.2Li₂MnO₃.0.8LiNi_(0.8)Co_(0.20)O₂ or 0.15Li₂TiO₃.0.85LiMnO₂. Other electrolytes well known in the art may be used. Laminated electrodes were made containing approximately 7 to 10 mg of the xLiMO₂.(1-x)Li₂M′O₃ powder, i.e., approximately 82% by weight of the laminate electrode, intimately mixed with approximately 10% by weight of a polyvinylidene difluoride (Kynar PVDF polymer binder) and approximately 8% by weight of a suitable carbon (i.e. graphite, such as Timcal SFG-6, or acetylene black, such as Chevron XC-72) in 1-methyl-2-pyrrolidinone (NMP). Other binders are well known in the art and may be substituted here. The slurries were coated with a doctor blade onto an aluminum foil substrate current collector. The coatings were dried in vacuum at temperatures from 70° C. for about 12 hours, and punched out as electrode laminates. Metallic lithium foil was used as the counter electrode. Li/xLiMO₂.(1-x)Li₂M′O₃ cells were discharged and charged at constant current (typically 0.1 mA/cm²) within the voltage range 4.5 to 2.0 V.

[0031] Typical electrochemical data for Li/xLiMO₂.(1-x)Li₂M′O₃ cells are provided in various plots, as shown in FIG. 5, a Li/0.2Li₂MnO₃.0.8LiNi_(0.8)Co_(0.2)O₂ cell; and FIG. 6, a Li/0.15Li₂TiO₃.0.85LiMnO₂ cell. For example, the electrode of Example 1, namely 0.2Li₂MnO₃.0.8LiNi_(0.8)Co_(0.2)O₂ has a theoretical electrochemical capacity of 212 mAh/g. The electrochemical data in FIG. 5 indicate that an initial capacity of approximately 208 mAh/g can be achieved from this electrode during the ‘break-in’ process on the initial charge of the cell and, thereafter, a steady rechargeable discharge capacity of approximately 136 mAh/g. For the stabilized 0.15Li₂TiO₃.0.85LiMnO₂ electrode of Example 3, as seen in FIG. 6, a capacity of 179 mAh/g was achieved during the ‘break-in ’ process on the initial charge of the cell, and thereafter a rechargeable capacity of 108 mAh/g was achieved.

[0032] The data in the examples provided above indicate that the principle of this invention can be used to stabilize LiMO₂ compounds with a Li₂M′O₃ component, and specifically those containing M═Ni and/or Mn that are of major significance and interest to the lithium battery industry for replacing the lithium-cobalt-oxide, LiCoO₂, as the electrode of choice, thereby reducing cost. The performance and effectiveness of the xLiMO₂.(1-x)Li₂MO₃ electrodes (O<x<1 ) of this invention depend on the concentration of the trivalent transition metal ions, M, in the structure, that is the value of “x” which preferably is equal to or greater than 0.8 and less than 1. A major advantage of the compounds of this invention is that the concentration of the trivalent M ions, the concentration of stabilizing tetravalent M′ ions and concentration of monovalent lithium ions can be tailored in such a way to extend and optimize both the capacity of the electrode as well as the stabilizing effect of the Li₂M′O₃ component in the structure. For example, an electrode with the composition 0.9LiMn_(0.9)Ni0.1O₂.0.1Li₂TiO₃ (alternatively Li_(1.2)Mn_(0.72)Ni_(0.08)Ti_(0.2)O_(2.2)) has a theoretical capacity of 252 mAh/g, which is only 8% less than that of LiCoO₂ used in state-of-the-art lithium cells.

[0033] This invention, therefore, relates to a lithium-metal-oxide positive electrode for a non-aqueous electrochemical lithium cell as shown schematically in FIG. 7, the cell represented by the numeral 10 having a negative electrode 12 separated from a positive electrode 16 by an electrolyte 14, all contained in an insulating housing 18 with suitable terminals (not shown) being provided in electronic contact with the negative electrode 12 and the positive electrode 16. Binders and other materials normally associated with both the electrolyte and the negative and positive electrodes are well known in the art and are not described herein, but are included as is understood by those of ordinary skill in this art. FIG. 8 shows a schematic illustration of one example of a battery in which two strings of electrochemical lithium cells, described above, are arranged in parallel, each string comprising three cells arranged in series.

[0034] While particular embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects. Therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention. 

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
 1. A lithium metal oxide positive electrode for a non-aqueous lithium cell prepared in its initial discharged state having a general formula xLiMO₂.(1-x)Li₂M′O₃ in which O<x<1, and where M is one or more trivalent ion with at least one ion being Mn, and where M′ is one or more tetravalent ion.
 2. A lithium metal oxide positive electrode according to claim 1 in which 0.8≦x<1.
 3. A lithium metal oxide positive electrode according to claim 1 in which 0.9≦x<1.
 4. A lithium metal oxide positive electrode according to claim 1 in which M and M′ are disordered in the electrode structure.
 5. A lithium metal oxide positive electrode according to claim 1 in which M′ is selected from Mn, Ti and Zr.
 6. A lithium metal oxide positive electrode according to claim 1 in which M is Mn and M′ is selected from at least one of Mn, Ti and Zr.
 7. A lithium metal oxide positive electrode according to claim 6 in which M, Mn, and M′ is Ti.
 8. A lithium metal oxide positive electrode according to claim 1 in which M, and M′ ions are partially replaced by mono- or multivalent cations.
 9. A lithium metal oxide positive electrode according to claim 8 in which M, and M′ ions are partially replaced by Mg²⁺ or Al³⁺ ions.
 10. A lithium metal oxide positive electrode according to claim 1 in which the lithium ions are partially replaced by H⁺ cations.
 11. A hydrothermal method for synthesizing a lithium metal oxide positive electrode xLiMO₂.(1-x)Li₂M′O₃ in which 0<x<1, and where M is one or more trivalent ion with at least one ion being Mn, and where M′ is one or more tetravalent ion, in which the synthesis occurs in an autoclave, at a pressure between 5 and 35 atmospheres and at a temperature between 100 and 250° C.
 12. A method according to claim 11 in which the pressure is between 10 and 20 atmospheres and the temperature is between 180 and 230° C.
 13. A method according to claim 11 in which M is Mn and M′ is Ti.
 14. A lithium metal oxide positive electrode for a non-aqueous lithium cell prepared in its initial discharged state having a general formula xLiMO₂.(1-x)Li₂M′O₃ in which 0<x<1, and where M is one or more trivalent ion with at least one ion being Ni, and where M′ is one or more tetravalent ion with at least one ion being Mn.
 15. A lithium metal oxide positive electrode according to claim 14 in which 0.8≦x<1.
 16. A lithium metal oxide positive electrode according to claim 14 in which 0.9≦x<1.
 17. A lithium metal oxide positive electrode according to claim 14 in which M and M′ are disordered in the electrode structure.
 18. A lithium metal oxide positive electrode according to claim 14 in which M ions are Ni and Co, and M′ is Mn.
 19. A lithium metal oxide positive electrode according to claim 14 in which M is Ni and M′ is Mn.
 20. A lithium metal oxide positive electrode according to claim 14 in which M and M′ ions are partially replaced by mono- or multivalent cations.
 21. A lithium metal oxide positive electrode according to claim 20 in which M and M′ ions are partially replaced by Mg²⁺ or Al³⁺ ions.
 22. A lithium metal oxide positive electrode according to claim 14 in which the lithium ions are partially replaced by H⁺ cations.
 23. An electrochemical cell having a negative electrode and a non-aqueous electrolyte and a positive electrode, said positive electrode having in its initial discharged state, a general formula xLiMO₂.(1-x)Li₂M′O₃ in which 0<x<1, and where M is one or more trivalent ions having at least one ion being Mn and where M′ is one or more tetravalent ions.
 24. An electrochemical cell having a negative electrode and a non-aqueous electrolyte and a positive electrode, said positive electrode having in its initial discharged state a general formula xLiMO₂.(1-x)Li₂M′O₃ in which 0<x<1, and where M is one or more trivalent ions at least one ion being Ni and where M′ is one or more tetravalent ions with at least one ion being Mn.
 25. A battery consisting of a plurality of cells, at least some cells including a negative electrode and a non-aqueous and a positive electrode, said positive electrode in its initial discharged state, a general formula xLiMO₂.(1-x)Li₂M′O₃ in which 0<x<1, and where M is one ion being Mn and where M′ is one or more tetravalent ion connected in series and/or in parallel.
 26. A battery consisting of a plurality of cells, at least some cells including a negative electrode and a non-aqueous electrolyte and a positive electrode, said positive electrode having in its initial discharged state a general formula xLiMO₂.(1-x)Li₂M′O₃ in which 0<x<1, and where M is one or more trivalent ions at least one ion being Ni and where M′ is one or more tetravalent ions with at least one ion being Mn. 